According to foreign military information publications [Sohu], the Russian military deployed additional air defense to northern Syria, Eurasia Diary reports citing BulgarianMilitary.com
“The maximum detection range of the S-400 air defense radar at the Khmeimim base is only 600 kilometers, which means that the Russian S-400 radar can only detect aircraft over most of the border between Iraq and Syria, but not over the border between Iraq and Iran. The most appropriate explanation is that the Russian Air Force sent the 96L6E radar, located at the Khmeimim airbase, to the Kamyshli air base in the border region in northeast Syria, which is only 100 kilometers from the Iraqi border. First, the northern Iraqi airspace will be in the hands of the Russian Ministry of Defense. If F-35A belonging to the US Air Force appeared in the northern Iraqi airspace near the Iranian border in the early hours of January 11, they were probably tracked by Russia,” the Sohu news agency reported.
Earlier, the Russian Foreign Minister did report that Russian air defenses were able to detect several fifth-generation F-35 fighters near the Iranian border, which appeared here only a few hours after the rocket fire on American military bases in Iraq.
“At that time, there were at least six F-35s in the air, on the border, near Iranian airspace. This information still requires rechecking, but emphasizes the whole nervousness of the situation,” Lavrov said.
Given the Russian S-400’s target detection range, these air defense systems could indeed detect six a-35 fighters near Iran’s borders.